i3status is a small program (about 1500 SLOC) for generating a status
bar for dzen2, xmobar or similar programs. It is designed to be very
efficient by issuing a very small number of system calls, as one
generally wants to update such a status line every second. This ensures
that even under high load, your status bar is updated correctly. Also,
it saves a bit of energy by not hogging your CPU as much as spawning the
corresponding amount of shell commands would.
